The specificity of the antibody response of the mouse was determined by comparing the increase in total immunoglobulin production with immunogen-reactive antibody subsequent to antigenic challenge. Since the increase in both of these constituents was similar, it is concluded that the in situ antibody response is specific. The capacity of hamster female protein (FP) to activate complement was demonstrated. This further establishes the human C-reactive protein/amyloid P component functional chimerism of hamster FP thereby extending the potential biological activities of FP to include enhanced phagocytosis, cytolysis and inflammation.